1. Field of the Invention
The present invention relates to a medical stand capable of always balancing the weight of a load and maintaining an attitude of the load, and particularly, to a torque transmitting mechanism for maintaining an attitude of such a medical stand, capable of suppressing small vibrations occurring in the torque transmitting mechanism.
2. Description of the Related Art
A medical stand is an apparatus used to move a medical tool or a load to an optional position and keep the same at the position. A typical example of the medical stand is disclosed in Japanese Unexamined Patent Application Publication No. 6-197912. The medical stand disclosed in this publication is designed to support a medical tool such as a surgical microscope and has a mechanism for always balancing the weight of the medical tool wherever the medical tool is moved and a mechanism for maintaining an attitude or orientation of the medical tool with respect to a reference plane wherever the medical tool is moved to.
FIG. 1 is a model view showing parallel linkages employed by the medical stand according to the above-mentioned related art. Among the parallel linkages, a first parallel linkage P1 includes two longitudinal links k1 and k2 and two lateral links k3 and k4. At an intermediate point 19 of the link k1, the first parallel linkage P1 is supported by a body of the medical stand (not shown) that is positionally fixed to a reference plane F such as a floor surface. The links k2 and k4 are rotatably connected to each other with a shaft as a joint β3 that supports a counterweight W. The links k3 and k1 are rotatably connected to each other with a joint β1. The link k3 is integral with a lateral link k8 that is rotatably connected to a joint β5 for supporting a load L. The load L is a medical tool in the embodiment. According to the principle of a parallel linkage, the counterweight W, the intermediate joint 19, and the load supporting joint β5 are always on a virtual straight line L1. Wherever the load L is positioned, the first parallel linkage P1 balances the weight of the load L with the counterweight W around the joint 19 serving as a fulcrum.
A second parallel linkage P2 includes the longitudinal link k1 common to the first and second parallel linkages P1 and P2, a longitudinal link k5, and two lateral links k6 and k7. The link k6 is fixed relative to the medical stand body (not shown). A third parallel linkage P3 includes two longitudinal links k10 and k11 and two lateral links k8 and k9. The link k8 is integral with the link k3 of the first linkage P1. The joint β1 is a common joint to the first, second, and third parallel linkages P1, P2, and P3. The link k10 of the third parallel linkage P3 is coupled with the link k7 of the second parallel linkage P2 through a crank or a connecting element 134. The orientation of a primary axis of the front link k11 with respect to the lateral link k6 is thus always fixed through the third parallel linkage P3, crank 134, and second parallel linkage P2. As a result, the front link k11 is always oriented plumb (gravity direction g) wherever the load L is moved to. The center of gravity Mc of the load L is right below the joint β5 at a lower end of the front link k11. The second parallel linkage P2, crank 134, and third parallel linkage P3 form a torque transmitting mechanism acting between the link k6 fixed to the medical stand body and the link k11 supporting the load L. The joints 19, β1, and β5 are equivalent to one another in terms of torque transmission. The direction of plumb mentioned above is in parallel with the direction of gravitational force and includes, for example, centrifugal force.
In this way, the medical stand shown in FIG. 1 employs very simple mechanisms to maintain the weight balance of the load L such as a surgical microscope wherever the load L is moved and also keep a posture or tilt of the load L.
When a surgeon conducts a microscopic operation on a patient by observing an enlarged image of an affected part provided by a surgical microscope supported on the medical stand, the medical stand maintains the weight balance of the surgical microscope that usually weighs over 20 kg, allows the surgeon to easily move the surgical microscope to a required position and stop the same at the position, and provides the surgeon with stabilized images of the affected part by maintaining an attitude (tilt) of the surgical microscope during the movement of the surgical microscope.